Staple driving apparatus



H. E. BADE May 23, 1967 STAPLE, DRIVING APPARATUS 2 Sheets-Sheet 1 Filed June 5, 1965 INVENTOR. Heinz E B y 23, 1967 H. E. BADE 3,320,860

STAPLE DRIVING APPARATUS Filed June 5, 1965 2 Sheets-Sheet INVENTOR. Heinz E Bade United States Patent Oflice 3,320,860 Patented May 23, 1967 3,320,860 STAPLE DRIVING APPARATUS Heinz Emil Bade, HamburgGarstedt, Germany, assignor to .1011. Friedrich Behrens Maschinenfahrik, Ahrensburg, Holstein, Germany Filed June 3, 1965, Ser. No. 461,070 Claims priority, application Germany, Dec. 28, 1964, 13 79,920 12 Claims. (Cl. 91-461) The present invention relates to a pneumatically operable driving device for driving fastening means such as staples, nails and the like, into work pieces.

It is an object of this invention to provide a pneumatically operably driving device which will be substantially free from fluid pressure recoil at the end of the working stroke of the device.

It is another object of this invention to provide 'a pneumatically operable driving device of the above-mentioned general type in which the driving or working stroke will start immediately at full force.

It is a further object of this invention to provide a driving device as set forth in the preceding paragraphs, which is particularly simple in construction and operation and does not require any springs.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIGURE 1 is a vertical section through a driving device according to the present invention in its operative position immediately prior to the start of the driving stroke;

FIGURE 2 shows the driving device of FIGURE 1 during its driving stroke;

FIGURE 3 represents a section taken along the line III-III of FIGURE 2;

FIGURE 4 represents a section IV-IV of FIGURE 2.

The driving device according to the present invention is characterized primarily in that the working cylinder for the driver piston and the control piston for opening and closing the interior of the working cylinder with regard to the atmosphere are mechanically interconnected and together form a central control member automatically initiating all control movements.

According to a particularly favorable arrangement, the working cylinder is provided with a flange having inserted therein said control piston while said cylinder is, below said flange, provided with slots to be opened and closed with regard to a compressed air reservoir and to the interior of the cylinder.

A practical embodiment of the present invention as illustrated in the drawing and comprises a main cylinder housing 1 having cast thereon a handle housing 2 which latter forms an air chamber or reservoir 3 adapted to store air under pressure for actuating the driving machine or staple driver shown in the drawing. Housing 2 is provided with a fitting 4 for connection with a hose (not shown) for connecting reservoir 3 to a source of compressed air.

The staple driver also comprises a connecting member 5 cast onto housing 2 and adapted to receive a fastener support 7 of any standard design for feeding the fasteners into the driving part proper. The said connecting member 5 connects the tail end of said handle housing 2 with the lower portion of cylinder housing 1.

The upper end of cylinder housing 1 has mounted thereon and fixedly connected thereto a cap 8 with a gasket 9 thereon adapted to seal the upper end of cylinder housing 1. One or more longitudinal bores 10 lead into a chamber 11 defined by housing 1 and a cylinder 12.

taken along the line Cylinder 12 is axially displaceably mounted in housing 1 by means of reinforced end portions 12a, 12b sealingly engaging said cylinder housing 1. The upper end of cylinder 12 is provided with a flange 13. Cylinder 12 with its reinforced end portions 12a, 12b and flange 13 form one integral turned piece produced during one and the same machining operation so that reinforced portions 12a, 12b and flange 13 are in proper alignment with each other. Thus, cylinder 12 is guided in housing 1 by flange 13 and reinforced end portions 12a, 12b in such a manner that tilting and jamming of cylinder 12 in housing 1 is prevented.

Flange 13 has inserted thereinto an insert 14, for instance by slide fitting insert 14 into and connecting the same to flange 13 of the cylinder 12 by means of a locking ring 15. Insert 14 has an upwardly extending hub 16 which is provided with a sealing ring or O-ring 17 and is slidable in a bore 18 of cap 8 which latter carries an elastic plate or seal 19, for instance of polyurethane or rubber material, which is adapted to engage and seal the upper end of the bore 20 in insert 14.. Insert 14 is provided with a magnet 22 and a cushioning member 22a, for instance of rubber material or any kind of plastic material. It will be appreciated that the lower end face of the cushioning member 22a when not engaged by the driver piston 32 protrudes somewhat beyond the end face of insert 14 as shown in FIG. 2. Flange 13 has provided therein an O-ring 24 while its bottom surface is provided with an annular groove and a seal 23, for instance of elastic rubber material, for sealing the upper end portion 25 of housing 1 and bore or bores 10. Flange 13 protrudes beyond the outer periphery of housing portion 25 and has an annular marginal surface 25 which is always subjected to the pressure in reservoir 3.

Below flange 13 cylinder 12 is furthermore provided with ribs 12' and radial slots 26 (see FIG. 3) which in the position illustrated in FIG. 1 of the drawing are closed by housing 1. However, when cylinder 12 is lifted to such an extent that hub 16 engages seal 19 (FIG. 2), slots 26 will extend above the end surface of housing portion 25 so as to communicate with reservoir or chamber 33. It is to be understood that insert 14 resets on the ribs 12'.

The bottom 27 of cylinder housing 1 has fixedly inserted therein a guiding member 28 secured by a nose 29 in housing 1 and provided with a slot 31} therethrough for guiding a driver 31 which has its upper end connected to the driver piston 32, 40 by means of a pin 33. The uppermost portion of slot 30 widens into a recess 34 which has such a depth that when driver 32, 40 occupies its fully retracted position, the lower end of driver 31 is withdrawn from slot 30 to such an extent that recess 34 establishes communication between the interior of cylinder 12 and the atmosphere through slot 30.

Guiding member 28, Which may consist for instance of polyurethane, is surrounded by an annular cushioning member 35 which may consist also of polyurethane or rubber material. The inner periphery of cushioning member 35 is spaced from the outer periphery of guiding member 28 so as to define therewith an annular path 36, whereas the outer periphery of cushioning member 35 which is provided with a lip 37 is under pro-load in frictional engagement with the lower inner wall portion of cylinder 12 so as to be movable therewith during the upward movement of cylinder 12. The lower end of cushioning member 35 is of a diameter less than that of lip 3'7 to an extent depending on the elasticity or resiliency of the material. A reduced diameter portion 38 of member 35 protrudes beyond lip 37 to protect the same from being engaged by surface 39 of driver piston portion 40.

The piston for actuating driver 31 comprises a metallic Jody portion 32 and an elastic body portion 40 preferibly made of polyurethane. Pin 33 is journalled in :lastic body portion 40 and passes with slight play through Jody portion 32. In this way pin 33 is protected against damaging shearing forces.

Elastic body portion 46 serves for cushioning the impact of the driver piston on member 35 not only during its normal working stroke but also in case the driving apparatus is operated when not in engagement with a work piece. A sealing ring 4th: is interposed between piston portions 32 and 40. As will be seen from FIGS. 1 and 2, piston portions 32 and have an outer diameter smaller than the inner diameter of cylinder 12. Piston 32, 40 will be guided in cylinder 12 by sealing ring 4W. Due to this arrangement, metallic piston portion 32 will not engage the wall of cylinder 12 even if the piston should also move in radial direction during its upward or downward stroke. In this way, a harmful edging and canting movement of metallic piston portion 32 with regard to cylinder 12 is prevented. Sealing ring 40a is preferably made of Per bunan.

The top surface of the driver piston is provided with grooves 74 (FIG. 3) so that this top surface and the passages 26 are exposed to atmospheric pressure through passage 20, when the driver piston is in retracted position.

The lower end portion of cylinder 12 (when the lattter occupies its FIG. 1 position) is, slightly above the cushioning member 35, :provided with a plurality of radial bores 41 for establishing communication between chamber 11 and the interior of cylinder 12. Bottom 27 of cylinder housing 1 is provided with a plurality of circularly distributed passages 42 (one only being shown) for a purpose explained further below.

The operation of the staple driver shown in the drawing is controlled by a pin 43 in cooperation with a trigger 44. Pin 43 is reciprocable in a bushing 45 which is screwed into handle housing 2 and sealed by a seal 46. Pin 43 may be of triangular or quadrangular cross section while the bore of bushing 45 in which it is reciprocable is round so that pin 43 together with the wall of the bore in which it is reciprocable will define longitudinal passages or grooves 47 communicating with the atmosphere. Pin 43 is also provided with a seal 48 adapted in the position shown in FIG. 1 to seal said passages 47. Pin 43 is furthermore provided with a seal 49 adapted in the uppermost position of pin 43 to seal bore 50 communicating with the pressure chamber 3. The trigger 44 is connected to or forms a part of plate 5.1 pivotally supported by a pin 52 in housing 1. Plate 51 carries a first abutment pin 54 which limits the pivotal turning movement of trigger 44 in clockwise direction (with regard to the drawing), and also carries a second abutment pin 53 which will permit pulling of the trigger 44 in a certain working position only of the staple driving de vice, as will be explained further below. Trigger 44 is adapted to actuate control pin 43 so as to permit or interrupt communication between pressure chamber 3 and a passage 55 through bore 50. Passage 55 leads to a bore 56 in a tube 56a having reciprocably mounted therein a control member 57 with an annular groove'58. Tube 56a is provided with a conical portion 56 inserted into a corresponding control bore 56 in handle housing 2. This particular design has proved extremely successful in preventing leakage of compressed air.

The lower end of the control member 57 engages a pin 59 of a yoke member 60 with a lower end portion 61 at least partially surrounding the mouth of a staple guiding member 62 connected to fastener support 7. When the staple driving device is not in driving position, i.e. is not placed on a work piece into which a staple is to be driven, while air pressure prevails in bore 56, control member 57 through pin 59 holds yoke 60 downwardly so that member 61 protrudes in downward direction beyond member 62. In this position the upper portion 57a of member 57 prevents actuation of trigger 44. It is only when the staple driver is firmly pressed against a work piece that yoke through pin 59 pushes control member 57 upwardly thereby moving groove 53 into a position opposite pin 53 and permitting pulling of trigger 44.

Operation Assuming that all parts of the driver occupy the position shown in PEG. 1 and that it is now desired to actuate the driver, the operator places the staple driving device upon the work piece shown in FIG. 1 into which a staple is to be driven. As a result thereof, the lower end 61 of the yoke is pushed back until its lower end is substantially flush with the mouth of member 62. In view of this push-back movement of the lower end 61 of yoke 60, yoke 60 through the intervention of pin 59 guided in slot 67 has moved control member 57 upwardly so that annular groove 58 is now opposite abutment 53. The operator is now able to pull the trigger 44 (FIG. 2) and does so by tilting plate 51 in counter-clockwise direction, i.e. lifting trigger 44. As a result thereof, trigger 44 causes control pin 43 to close opening Stt so that passage 55 will communicate with the outside through passage 47. Consequently, the air under pressure in bores 56 and 63 and passage 64 as well as in chamber 66 will be exhausted.

On the other hand, the pressure in chamber 3 acting on the bottom or lower marginal portion 25 of flange 13 will push flange 13 and thereby clyinder 12 upwardly so that its hub 16 engages seal 19 and will be sealed thereby. As a result thereof, bore 20 which previously communicated with the atmosphere through a mufiling bushing 69, e.g. of porous synthetic material and provided with bores 69a and passages 68, is closed toward the outside, and slots 26 in cylinder 12 now communicate with chamber 3 since, as mentioned above, cylinder 12 with its flange 13 has been moved upwardly so that flange 13 with seal 23 has been lifted off from upper end portion 25 of the housing 1. The air pressure in chamber 3 immediately separates the piston portion 32 from the surface of the insert 14 when compressed air passes through the grooves of the piston surface 74 and the bottom surface 70 of insert 14 against the holding force of the magnet 22 and pushes the driver piston downwardly instantaneously. Grooves 74 are so designed that piston 32, 40 is separated from magnet 22 only after cylinder 12 with flange 13, has been moved upwardly to the position shown in FIG. 2 in which slots 26 have been completely opened.

Inasmuch as bore '20 in insert 14 is closed in view of the abutment of top surface 72 of hub 16 against sealing ring 19, piston 32, 40 is, immediately following its detachment from magnet 22, subjected to the full force of the compressed air. Therefore, driver piston 32, 40 executes its driving stroke right from the start with high initial speed and full force. Piston 32, 40 transmits a short forceful blow on a staple located in the path of driver 3&1 whereby, so-to-speak, a mechanical shock wave is transmitted from the head or shank end of the staple to the tip thereof without causing any bending stresses on the shank or leg portions of the staple. Simultaneous ly, air under pressure passes from chamber 3 through bore or bores 10 into chamber 11 and builds up pressure in said chamber. As will be evident from the drawing, bores 10 end at the bottom surface of flange 13 and are, therefore, opened only in the lifted position of flange 13, i.e. during the working stroke of the driving device. Since, as mentioned above, cylinder 12 was pushed upwardly, also the cushioning member 35, which is frictionally mounted with the lip 37 in the lower portion of cylinder 12, is moved upwardly together with cylinder 12 so that the annular passage 36 communicates with the outside through the passages 42 in the cylinder bottom 27. During its downward movement, driver piston 32, 40 pushes the air below said piston through the now widened annular passage 36 and through bores 42 into the atmosphere. The widened annular passage 36 and the bores 42 are of such dimensions that under no circumstances can a counter pressure build up below piston 32, 40 during its working stroke.

When the driver piston 32, 40 during its downward or Working stroke impacts upon cushioning member 35, it overcomes the frictional engagement of cushioning member 35 with cylinder 12 and pushes cushioning member 35 downwardly against the bottom 27 of cylinder housing 1 while closing off bores 42. In this position of the driver piston, the latter closes otf bores 41 because the cylinder 12 is still up as long as the trigger 44 is pulled, i.e. as long as chamber 66 communicates with the atmosphere. When trigger 44 is released, the pressure in chamber 3 pushes pin 43 downwardly, thereby opening the bore '50, whereas the seal 48 on pin 43 closes exhaust passage 47. Air under pressure now rushes through passage 55, bores 56, 63 and 64 into chamber 66 and pushes insert 14 and cylinder 12 with flange 13 downwardly back into FIG. 1 position. This is due to the fact that the force acting upon the upper surface 13' of flange 13 and the upper marginal surface 14' of insert 14 is greater than the force acting upon the bottom surface 13" of flange 13 and the bottom surface 70 of insert 14 since the total area of surfaces 13 and I14 is larger than that of surfaces 13" and 70 minus the area of the surfaces 12 (cross section of ribs) of cylinder 12 between and within the range of slots 26. As will be evident from the above, the control member =12, 14 is held in engagement with housing portion 25 exclusively due to the effect of the compressed air in chamber 66 on the top surface 13 of flange 13 and on the top surface 14 of the marginal portion of insert 14.

In view of the elasticity of sealing body 35, which is preferably made of polyurethane, drive-r piston 32, 40 rebounds upon impact on said sealing body. Meanwhile, due to the flow of compressed air through bore .10, air pressure builds up in chamber 11. Compressed air then flows from chamber 11 through bores 41 underneath piston 32, 40 and will push the latter upwardly until it abuts the magnet 22 and cushioning member or members 22a in insert 14. At this instant, piston 32, 40 is held in its upper position by the permanent magnet 22. As a result of the downward movement of cylinder 12, bore 20 is vented through passage 68. In other words, the air which during the return stroke of piston 32, 40 is being displaced by the upper end face of piston portion 32, can easily escape through bore 20, bores 69a of bushing 69, and passage 68. It will be appreciated that surface 72 of hub 16 was spaced from seal 19 at the time when insert 14 with cylinder flange 1 3 was pushed downwardly. Since, as mentioned above, air under pressure now again fills that portion of bore 56 which is above end surface 73 of control member 57, the said air under pressure will push control member 57 downwardly as soon as the staple driving device, after completion of its working stroke, has been lifted off the work piece. Consequently, the end portion 61 of yoke 60 will again protrude beyond the mouth of member 62. In its downward position, control member 57 again has its upper larger diameter area in engagement with abutment 53 which latter thus prevents the triggering of the device until the device has been placed upon a work piece. At the end of its return stroke, the driver 31 is withdrawn into recess 34 in the driver guiding member 28 to such an extent that if any air under pressure should still be present in cylinder 12 below piston 32, this air will be vented into the atmosphere through said recess 34 and slot 30. This venting of the cylinder space below the driver piston 32 is of particular importance when the driving operations or working strokes follow each other very quickly. It will be appreciated that any counter pressure below the driving piston during the working stroke must be avoided inasmuch as it would counteract the driving strokes.

The elements of the device now have again reached their starting position and are ready for the next working cycle as soon as the device is again placed on a new area of the work piece into which a staple is to be driven.

As will be evident from the foregoing description, one of the most outstanding features of the present invention consists in that the cylinder in which the driver piston is reciprocable is itself reciprocable and in cooperation with the housing portion in which the cylinder is reciprocable forms control means for either venting the driving side of the driver piston during the retraction stroke of the latter or closing the venting passage for said driving side while establishing communication between said driving side and the fluid pressure reservoir to thereby bring about the working stroke of the driver piston. This arrangement not only greatly simplifies the construction of the driving device according to the present invention over heretofore known devices requiring special mechanisms for performing the control action effected by the reciprocable cylinder of the present invention, but also makes the device according to the present invention less liable to failures. Also the height of the driving device according to the present invention is greatly reduced over heretofore known devices of the type involved.

It is, of course, to be understood that the present invention is, by no means, limited to the particular construction shown in the drawings, but also comprises any modifications within the scope of the appended claims. Thus, if desired, bore or bores 10 may be provided with a re turning valve of any standard design which remains open only until the pressure in chamber 11 equals the pressure in chamber 3. When this pressure equalization occurs, the said returning valve closes, whereas it opens again when a pressure drop from chamber 3 to chamber 11 occurs.

Similarly, while the driver piston 32 has been Composed of an upper metallic member 32 and a member 40, preferably of polyurethane, it is, of course, also possible to design the driver piston 32 differently without in any Way affecting the essence of the present invention.

What I claim is:

1. In a pneumatically operable driving device having a reciprocable driving piston with a driving side adapted when subjected to pneumatic pressure to perform a working stroke, which comprises: a housing having a head portion and a handle portion and including a reservoir adapted to receive air under pressure, said head portion being provided with venting means and including a tubular wall having one end provided with an annular end face, a cylinder body reciprooably receiving said piston and being reciprocable in said tubular wall and having a radially outwardly extending flange portion at that end thereof which is adjacent said end face, the outer diameter of said flange portion being in excess of the outer diameter of said end face, said cylinder body also being provided with passage means therethrough adjacent said flange portion for communication with the driving side of said piston, a cover member arranged inside said flange portion and firmly connected to said cylinder body so as to be movable therewith, said cover member being provided with means for controlling said venting means, said flange portion together with said cover member forming a pneumatically operable differential piston for moving said cylinder body into a first position in which a portion of said flange portion engages said end face while said passage means is closed by said tubular wall and said venting means is open and into a second position in which said flange portion disengages said end face and said passage means communicates with said driving side and said reservoir while said cover member closes said venting means, and vice versa, that flange side facing said end face forming a portion of the smaller surface of said differential piston and being in continuous communication with said reservoir, and control means for controlling communication of the larger surface of said diiferential piston with said reservoir and with the atmosphere.

2. An arrangement according to claim 1, in which the :maller surface portion of said differential piston has :ealing means therein within the range of and for engagement with said end face of said tubular wall.

3. An arrangement according to claim 1, in which said :over member has a cylindrical hub portion with venting :hannel means therethrough.

4. An arrangement according to claim 1, in which said driving piston also has a retraction side, and in which aaid cylinder body comprises two axially spaced end poriions respectively slidably received in two axially spaced portions of said tubular wall and also comprises an intermediate portion located between said two end portions and with the adjacent portion of said tubular wall defining an annular chamber, conduit means provided in said cylinder body and operable at the end of the working stroke of said piston to establish communication between said annular chamber and the retraction side of said driving piston, and throttling conduit means arranged in said tubular wall and controlled by said cylinder body for establishing communication between said driving side and said annular chamber at the start of the working stroke of said piston.

5. An arrangement according to claim t, in which said throttling conduit means leads from said annular chamher to said end face, whereby said throttling conduit means communicates with said driving side in said second position only of said cylinder body in which position said flange portion disengages said end face.

6. An arrangement according to claim 1, in which said venting means includes sealing means adapted to be engaged by a portion of said cylinder body for closing said venting means.

7. An arrangement according to claim 1, in which the passage means in said cylinder body are formed by segmental slots.

8. A pneumatically operable driving device, which includes: a housing with a reservoir adapted to receive air under pressure, a cylinder body reciprocable in said housing, and a pneumatically operable piston reciprocable in said cylinder body from a retracted position to a driving position and vice versa and having a driving side operable when subjected to pneumatic pressure to cause said piston to perform a working stroke, said cylinder body being provided with double acting pneumatically operable piston means for controlling the initiation of said working stroke of said piston and having a surface portion facing said driving side and provided with a permanent magnet for holding said piston in its retracted position, said double acting pneumatically operable piston means being operable selectively to move said cylinder body into a first position for establishing communication between said reservoir and said driving side to thereby cause said piston to perform a working stroke and into a second position for interrupting said communication and venting said driving side to permit said piston to move to its retracted position.

9. A pneumatically operable driving device, which includes: a housing having a first portion with a reservoir adapted to receive air under pressure and having a second portion including a tubular member having a bottom and being open at that end which is opposite said bottom, said tubular member being provided wit-h exhaust opening means adjacent said bottom, said second portion also including cover means arranged in spaced relationship to said open end and provided with venting means, a cylinder reciprocable in said tubular member and including a head interposed between said open end and said venting means, a pneumatically operable driver piston reciprocable in said cylinder and provided with a driver protruding therefrom, said head forming a differential piston with the smaller piston surface thereof in continuous communication with said reservoir, control means interposed between the larger surface of said differential piston and said reservoir and operable to control communication of said larger differential piston surface with said reservoir and with the atmosphere, said differential piston also having firmly connected thereto means operable to close and open said venting means, passage means extending through said cylinder on that side of said differential piston which forms the smaller differential piston surface, said differential piston being operable by pneumatic pressure to move said cylinder into a first position in which i said passage means is within said tubular member and closed thereby with regard to said reservoir while the smaller differential piston surface is in sealing engagement with the adjacent end face of said tubular member and while said venting means is in open position, said differential piston also being operable by pneumatic pressure thereon to move to a second position in which the smaller differential surface has disengaged said tubular member and said passage means is out of said tubular member while said venting means is closed by said cylinder head, that end of said cylinder which is adjacent said bottom closing said exhaust opening means when said cylinder is in its first position and freeing said exhaust opening means when said cylinder is in its second position, a first insert connected to said bottom and including guiding slot means for guiding the free end of said driver, and a second insert surrounding said first insert in spaced relationship thereto and having an outer peripheral lip extending radially outwardly and engaging under preload the inner surface of the adjacent cylinder end, said second insert being movable relative to said cylinder when impacted upon by said driver piston to thereby sealingly engage said bottom, said second insert also being movable with said cylinder so as to disengage said bottom when said cylinder moves to its second position, said second insert also being operable to be lifted off said bottom in response to said cylinder moving to its second position to thereby free said exhaust opening means,

10. An arrangement according to claim 9, in which said first and second inserts confine with each other an annular conical passage flaring in the direction toward said bottom.

11. An arrangement according to claim 9, in which said second insert has that surface thereof which faces said driver piston provided with an elevation having its periphery spaced from said cylinder.

12. A pneumatically operable driving device, which includes: a housing with a reservoir adapted to receive air under pressure and with venting means communicating with the atmosphere, a cylinder body reciprocable in said housing, a pneumatically operable driver piston reciprocable in said cylinder body and having a driving side operable when subjected to pneumatic pressure to cause said driver piston to perform a working stroke, said cylinder body including a pneumatically operable control piston firmly connected to said cylinder body and having an extension for cooperation with said venting means, said venting means including a rnufiling bushing with perforations and also including sealing means, said extension being adapted to enter said bushing and engage said sealing means to thereby close said perforations to close said sealing means, said extension having a bore therethrough and leading into the interior of said cylinder body, said control piston being operable to move said cylinder body selectively into a first position for causing said driver piston to perform a working stroke and into a second position for permitting said driver piston to carry out a return stroke, said cylinder body being provided with passage means therethrough open in said first position for communication with said reservoir and closed in said second position, said control piston having a first surface in continuous communication with said reservoir and having a second surface opposite said first surface and facing away therefrom, and control means interposed between said second surface and said reservoir and operable selectively to establish communication of said sec- 9 end surface with the atmosphere while preventing communication of said second surface with said reservoir to thereby move said cylinder body into said first position and establish communication between said reservoir and said driving side through said passage means, said control means also being operable selectively to establish communication between said second surface and said reservoir while preventing communication between said second surface and the atmosphere to thereby move said References Cited by the Examiner UNITED STATES PATENTS Doyle.

Juilfs 91-461 Wandel.

Goldring 92-85 Powers et a1. 2271-30 Volkman 92-85 cylinder body into said second position while preventing 10 MARTIN SCHWADRON Pfimary Examine,"

P. T. COBRIN, B. L. ADAMS, Assistant Examiners.

communication of said passage means with said reservoir. 

1. IN A PNEUMATICALLY OPERABLE DRIVING DEVICE HAVING A RECIPROCABLE DRIVING PISTON WITH A DRIVING SIDE ADAPTED WHEN SUBJECTED TO PNUEMATIC PRESSURE TO PERFORM A WORKING STROKE, WHICH COMPRISES: A HOUSING HAVING A HEAD PORTION AND A HANDLE PORTION AND INCLUDING A RESERVOIR ADAPTED TO RECEIVE AIR UNDER PRESSURE, SAID HEAD PORTION BEING PROVIDED WITH VENTING MEANS AND INCLUDING A TUBULAR WALL HAVING ONE END PROVIDED WITH AN ANNULAR END FACE, A CYLINDER BODY RECIPROCABLY RECEIVING SAID PISTON AND BEING RECIPROCABLE IN SAID TUBULAR WALL AND HAVING A RADIALLY OUTWARDLY EXTENDING FLANGE PORTION AT THAT END THEREOF WHICH IS ADJACENT SAID END FACE, THE OUTER DIAMETER OF SAID FLANGE PORTION BEING IN EXCESS OF THE OUTER DIAMETER OF SAID END FACE, WITH CYLINDER BODY ALSO BEING PROVIDED WITH PASSAGE MEANS THERETHROUGH ADJACENT SAID FLANGE PORTION FOR COMMUNICATION WITH THE DRIVING SIDE OF SAID PISTON, A COVER MEMBER ARRANGED INSIDE SAID FLANGE PORTION AND FIRMLY CONNECTED TO SAID CYLINDER BODY SO AS TO BE MOVABLE THEREWITH, SAID COVER MEMBER BEING PROVIDED WITH MEANS FOR CONTROLLING SAID VENTING MEANS, SAID FLANGE PORTION TOGETHER WITH SAID COVER MEMBER FORMING A PNEUMATICALLY OPERABLE DIFFERENTIAL PISTON FOR MOVING SAID CYLINDER BODY INTO A FIRST POSITION IN WHICH A PORTION OF 